Method for forming a liquid film on a substrate

ABSTRACT

A liquid film forming method of dropping a liquid from a dropping nozzle or dropping nozzles of a dropping unit onto a substrate to be processed, and then providing relative movement between the dropping unit and the substrate while keeping the liquid dropping on the substrate, so as to form a liquid film on the substrate.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is based upon and claims the benefit of priorityfrom the prior Japanese Patent Applications No. 11-272327, filed Sep.27, 1999; and No. 2000-255461, filed Aug. 25, 2000, the entire contentsof which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002] This invention relates to a liquid film forming method wherein aliquid is applied onto a substrate to be processed so as to form aliquid film.

[0003] In spin coating method, which has been used in lithographicsteps, almost all of a liquid dropped onto a substrate is dischargedoutside the substrate so that a film is formed from the remainderthereof, which is several percent of the liquid. Therefore, most of thedropped liquid is of no use. Since most of the liquid is discharged, anadverse effect is produced on environment. Moreover, there arises aproblem that in rectangle substrates or disc-shaped substrates having alarge diameter of 12 inches or more, turbulent air is generated at thecircumferential portion of the substrates so that the film thicknessuniformity of this portion becomes deteriorated.

[0004] As a method of applying a liquid uniformly onto the whole of asubstrate without vain use of the liquid, Jpn. Pat. Appln. KOKAIPublication No. 2-220428 describes a method of dropping a Resist frommany nozzles which are arranged along one line and, spraying from theback thereof, a gas or a liquid onto a film-forming surface to obtain auniform film. Jpn. Pat. Appln. KOKAI Publication No. 6-151295 describesa technique wherein many spray nozzles are made in a rod and a resist isdropped out from them onto a substrate in order to obtain a uniformfilm. Furthermore, Jpn. Pat. Appln. KOKAI Publication No. 7-321001describes a method of using a spray head in which many spray nozzles forspraying a resist are made and moving the head relatively to a substrateto perform application.

[0005] In all of these applicators, plural dropping or spraying nozzlesare arranged along one rank and they are scanned in order to obtain auniform film. Besides application methods using a device having thesenozzles, there is known a method of using a single liquid jetting-outnozzle and the nozzle is scanned over a substrate to be processed, so asto form a liquid film.

[0006] These methods have a problem that the processing time persubstrate becomes long dependently on a method of handling the nozzle(s)or the use amount of a liquid gets very large.

BRIEF SUMMARY OF THE INVENTION

[0007] An object of the present invention is to provide a liquid filmforming method making it possible to shorten processing time andsuppress the use amount of a liquid.

[0008] In order to attain the above-mentioned object, the presentinvention is as follows.

[0009] (a) A first aspect of the liquid film forming method according tothe present invention is a liquid film forming method of dropping aliquid adjusted to be spread into a give amount on a substrate to beprocessed from a dropping nozzle or dropping nozzles of a dropping unitonto the substrate, and then moving the dropping unit and the substraterelatively while keeping the liquid dropping on the substrate, so as toform a liquid film on the substrate,

[0010] wherein the relative movement of the dropping unit and thesubstrate is composed of straight movement along a file direction inwhich the dropping unit passes from one end side of the substratethrough an upper space of the substrate to the other end side of thesubstrate, and movement along a rank direction outside the substrate,

[0011] movement length along the file direction is the sum of droppinglength (L) over the substrate and length of an acceleration/decelerationsection, and

[0012] movement speed (v) along the file direction over the substrate isdefined dependently on the square root of the product of the droppinglength (L) and the absolute value of acceleration/deceleration (a)within the acceleration/deceleration section.

[0013] (b) A second aspect of the liquid film forming method accordingto the present invention is a liquid film forming method of dropping aliquid adjusted to be spread into a give amount on a disc-shapedsubstrate which is to be processed and has a diameter (D) has from adropping nozzle or dropping nozzles of a dropping unit above thesubstrate, and then moving the dropping unit and the substraterelatively while keeping the liquid dropping on the substrate, so as toform a liquid film on the substrate,

[0014] wherein the relative movement of the dropping unit and thesubstrate is composed of straight movement along a file direction inwhich the dropping unit passes from one end side of the substratethrough an upper space of the substrate to the other end side of thesubstrate, and movement along a rank direction outside the substrate,and

[0015] movement speed (v) along the file direction is defineddependently on the square root of the product of constant 0.4, thediameter (D) of the substrate, and the absolute value ofacceleration/deceleration (a) before and after the time when themovement speed (v) is given.

[0016] Preferred embodiments of the above-mentioned inventions are asfollows.

[0017] Dropping amount (W) from the dropping nozzle or the droppingnozzles of the dropping unit positioned over the substrate is defineddependently on an amount proportional to the movement speed (v).

[0018] The dropping unit has plural dropping nozzles and the droppingamount (W) is the total amount of the liquid dropped from all of thedropping nozzles.

[0019] The liquid is any one selected from an antireflection material, aresist material, a low dielectric material, an insulating material, awiring material and a metal paste.

[0020] The liquid film is formed, using the liquid having acharacteristic that when/a minute amount of the liquid is dropped onto aminute area of the substrate, a change amount of a contact angle of theliquid to the substrate is within +2 degrees during a time from 5seconds to 60 seconds after the dropping of the liquid.

[0021] (c) A third aspect of the liquid film forming method according tothe present invention is a liquid film forming method of dropping aliquid adjusted to be spread into a give amount on a substrate to beprocessed from a dropping nozzle or dropping nozzles of a dropping unitonto the substrate, and then moving the dropping unit and the substraterelatively while keeping the dropped liquid on the substrate, so as toform a liquid film on the substrate,

[0022] wherein the relative movement of the dropping unit and thesubstrate is composed of straight movement along a file direction inwhich the dropping unit passes from one end side of the substratethrough an upper space of the substrate to the other end side of thesubstrate, and movement along a rank direction outside the substrate, oris composed of spiral movement in which the dropping unit goes from thesubstantial center of the substrate to the periphery thereof or from theperiphery of the substrate to the substantial center thereof, and

[0023] a change amount of a contact angle of the liquid to the substrateis within ±2 degrees during a time from 5 seconds to 60 seconds afterthe dropping of the liquid when a minute amount of the liquid is droppedonto a minute area of the substrate.

[0024] A preferred embodiment of the above-mentioned invention is asfollows.

[0025] Control of the change amount of the contact angle of the liquiddropped onto the substrate to the substrate within ±2 degrees isattained by adjusting the ratio of a surfactant to a solvent and anapplication agent constituting the liquid.

[0026] (d) The liquid for application according to the present inventionis a liquid for application used in a liquid film forming method ofdropping the liquid adjusted to be spread into a give amount on asubstrate to be processed from a dropping nozzle or dropping nozzles ofa dropping unit onto the substrate, and then moving the dropping unitand the substrate relatively while keeping the dropped liquid on thesubstrate, so as to form a liquid film on the substrate,

[0027] comprising a solvent, an application agent, and a surfactant,

[0028] wherein the ratio of the surfactant to the solvent and theapplication agent is adjusted in such a manner that when a minute amountof the liquid is dropped onto a minute area of the substrate, a changeamount of a contact angle of the liquid to the substrate is within ±2degrees during a time from 5 seconds to 60 seconds after the dropping ofthe liquid.

[0029] (e) A fourth aspect of the liquid film forming method accordingto the present invention is a liquid film forming method of dropping aliquid adjusted to be spread into a give amount on a substrate to beprocessed from a dropping nozzle or dropping nozzles of a dropping unitonto the substrate, and then moving the dropping unit and the substraterelatively while keeping the liquid dropping on the substrate, so as toform a liquid film on the substrate,

[0030] wherein the relative movement of the dropping unit and thesubstrate is composed of straight movement along a file direction inwhich the dropping unit passes from one end side of the substratethrough an upper space of the substrate to the other end side of thesubstrate, and movement along a rank direction outside the substrate, oris composed of spiral movement in which the dropping unit goes from thesubstantial center of the substrate to the periphery thereof or from theperiphery of the substrate to the substantial center thereof, and

[0031] a dropping area is defined in such a manner that when the liquidfilm is spread by its fluidity, the liquid does not extend over aboundary step of the substrate film in the edge area of the substrate.

[0032] (f) A fifth aspect of the liquid film forming method according tothe present invention is a liquid film forming method of dropping aliquid adjusted to be spread into a give amount on a substrate to be,processed from a dropping nozzle or dropping nozzles of a dropping unitonto the substrate, and then moving the dropping unit and the substraterelatively while keeping the liquid dropping on the substrate, so as toform a liquid film on the substrate,

[0033] wherein the relative movement of the dropping unit and thesubstrate is composed of straight movement along a file direction inwhich the dropping unit passes from one end side of the substratethrough an upper space of the substrate to the other end side of thesubstrate, and movement along a rank direction outside the substrate, oris composed of spiral movement in which the dropping unit goes from thesubstantial center of the substrate to the periphery thereof or from theperiphery of the substrate to the substantial center thereof, and

[0034] relationship between the distance from a dropping start positionalong the rank direction to a boundary step of the edge of the substrateand that from a dropping finish position along the rank direction to theboundary step of the edge thereof is set so that the former distance islarge and the latter distance is small, and the distance between an endof the liquid film and the boundary step of the edge along the filedirection is set so as to gradually become smaller from the droppingstart position to the dropping finish position.

[0035] The present invention has the above-mentioned features so as tohave the following effects and advantages.

[0036] By deciding the movement speed along the file direction under theabove-mentioned conditions, it is possible to shorten the time forforming the liquid film on the substrate and suppress the use amount ofthe liquid.

[0037] Moreover, by deciding the dropping amount (W) from the droppingunit dependently on an amount proportional to the movement speed (v) ormaking the dropping amount constant, it is possible to make thethickness of the liquid film formed on the substrate uniform.

[0038] Additional objects and advantages of the invention will be setforth in the description which follows, and in part will be obvious fromthe description, or may be learned by practice of the invention. Theobjects and advantages of the invention may be realized and obtained bymeans of the instrumentalities and combinations particularly pointed outhereinafter.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

[0039] The accompanying drawings, which are incorporated in andconstitute a part of the specification, illustrate presently preferredembodiments of the invention, and together with the general descriptiongiven above and the detailed description of the preferred embodimentsgiven below, serve to explain the principles of the invention.

[0040]FIG. 1 is a view for explaining a liquid film forming method,using a single liquid supply nozzle, according to a first embodiment;

[0041]FIG. 2 is a view for explaining a movement pitch of the liquidsupply nozzle along the rank direction;

[0042]FIG. 3 is a view for explaining an acceleration section, adeceleration section and an equal speed section of the liquid supplynozzle along the file direction;

[0043]FIG. 4 is a graph of processing time to movement speed along thefile direction of the liquid supply nozzle (8 inch. Wafer);

[0044]FIG. 5 is a graph of consumption amount of a liquid to movementspeed along the file direction of the liquid supply nozzle (12 inch.Wafer);

[0045]FIG. 6 is a graph of processing time to movement speed along thefile direction of the liquid supply nozzle;

[0046]FIG. 7 is a graph of consumption amount of a liquid to movementspeed along the file direction of the liquid supply nozzle;

[0047]FIG. 8 is a graph showing appropriate movement speed to (substratesize X acceleration);

[0048]FIG. 9 is a graph showing movement speed to substrate position onthe basis of making the speed of each rank optimal;

[0049]FIG. 10 is a graph showing dropping amount to substrate positionon the basis of making the speed of each rank optimal;

[0050]FIG. 11 is a view showing the measuring state that the contactangle of an application liquid to a substrate to be processed in a thirdembodiment;

[0051]FIG. 12 is a graph showing the change of contact angle ofapplication liquids to a substrate to time after dropping;

[0052]FIG. 13 is a graph showing the change of contact angle ofapplication liquids to a substrate to time after dropping;

[0053]FIG. 14 is a graph showing the relationship between change amountof contact angle to time after dropping and thickness uniformity of asolid layer;

[0054]FIG. 15 is a view for explaining boundary step of the edge of asubstrate to be processed in a fourth embodiment;

[0055]FIG. 16 is a view for explaining a liquid film forming methodaccording to the fourth embodiment;

[0056]FIG. 17 is a sectional view along the rank direction showing aresist formed by dropping a liquid onto a resist-dropping area R of asubstrate to be processed;

[0057]FIG. 18 is a plan view showing measurement positions for obtainingthe profile of the thickness shown in FIGS. 19A and 19B;

[0058]FIGS. 19A and 19B are views each of which shows the profile of theresist thickness;

[0059]FIG. 20A is a view showing a state that an edge of a processedsubstrate and an edge of a liquid film at an application start side atthe time of dropping a liquid in the case of a conventional film formingmethod;

[0060]FIG. 20B is a view showing a state that the end of the processedsubstrate and the end of the liquid film at the application start sideat the time of finishing the formation of the liquid film in the case ofthe conventional film forming method;

[0061]FIG. 21A is a view showing a state that an end of the processedsubstrate and an end of the liquid film at an application finish side atthe time of dropping the liquid in the case of the conventional filmforming method;

[0062]FIG. 21B is a view showing a state that the end of the processedsubstrate and the end of the liquid film at the application finish sideat the time of finishing the formation of the liquid film in the case ofthe conventional film forming method;

[0063]FIG. 22 is a view for explaining a state of the end of theprocessed substrate and the end of the liquid film in the case of/theliquid film forming method according to the fourth embodiment;

[0064]FIG. 23 is a view for explaining an example in which the liquidfilm forming method according to the fourth embodiment is applied to arectangle substrate;

[0065]FIG. 24 is a view showing the profile of the resist thicknessformed by a liquid film forming method according to a fifth embodiment;

[0066]FIG. 25A is a view for explaining the relationship between thethickness of the liquid film and the fluidity according to aconventional film forming method; and

[0067]FIG. 25B is a view for explaining the relationship betweenthickness of the liquid film and fluidity according to a film formingmethod of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0068] Referring to the attached drawings, embodiments of the presentinvention will be described.

[0069] [First Embodiment]

[0070] In the present invention, a liquid supply nozzle (a dropping unitor a dropping nozzle) and a substrate to be processed are relativelymoved to supply a liquid on the substrate. As shown in, for example,FIG. 1, a liquid supply nozzle (a dropping unit or a dropping nozzle) 12is being moved above a substrate 11 to be processed, which is put on anassistant plate 10, so that a liquid film is being formed.

[0071]FIG. 2 shows details that the liquid film 13 is formed. In FIG. 2,the liquid film 13 is successively formed from the left side of thepaper. The liquid supply nozzle 12 is reciprocated back and forth of thepaper (along the file direction), and the nozzle 12 is moved right(along the rank direction) by a movement pitch p at an end of thereciprocating motion.

[0072] The movement speed along the file direction changes as shown inFIG. 3. That is, the nozzle 12 is accelerated at an acceleration (a) upto a speed (v) [=a×t wherein t is an acceleration time] inside anacceleration section. Thereafter, the nozzle 12 is moved at an equalspeed of the speed (v) over the substrate 11. Furthermore, the nozzle 12is decelerated at an acceleration (−a) to a speed of zero inside adeceleration section. Using the length (L) that the nozzle 12 passesover the substrate 11, the movement speed thereof (v), the acceleration(a) inside the acceleration section (a first run-up section in anadvance path, and a second run-up section in a return path), theacceleration (−a) inside the deceleration section (the second run-upsection in the advance path, and the first run-up section in the returnpath), processing time (t) necessary for one file is represented asfollows: $\begin{matrix}{t = {\frac{L}{v} + {2\frac{v}{a}}}} & (1)\end{matrix}$

[0073]FIG. 4 shows processing time for a single wafer, which is adisc-shaped 8-inch (20 cm) wafer, when the wafer is moved at themovement speed (v) having an acceleration of 12G, 15G or 18G (G=9.8m/sec²). A movement pitch (p) is set to 0.33 mm. The movement pitch (p)is not limited to 0.33 mm so far as the movement pitch makes it possiblethat when the liquid jetted out onto a plane surface is sufficientlyspread and the resultant liquid film is dried so that solid contentsthereof form a film, the film becomes substantially flat. FIG. 4 doesnot demonstrate that as the movement (scan) speed along the filedirection becomes higher, the processing time becomes shorter, butdemonstrates that the movement speed along the file direction forshortening the processing time has an optimal value (minimum value).This is because acceleration/deceleration length (time) becomes longeras the movement speed becomes higher.

[0074] The optimal value of the movement speed for shortening theprocessing time varies dependently on acceleration (deceleration). Asacceleration (deceleration) is larger, the optimal value of the movementspeed becomes larger. The processing time does not change very much evenif the movement speed is made more than the optimal value. However, ifthe movement speed is made large, the use amount of the liquid increaseshighly as shown in FIG. 5 since the liquid is supplied even within theacceleration (deceleration) section. The vertical axis of FIG. 5represents the value of (use liquid amount/substrate liquid amount), andmeans that as this value is larger, the vainness of the liquid islarger. In the case that the value of (use liquid amount/substrateliquid amount) is 2, the amount of the liquid discharged out of thesubstrate equal to the amount of the liquid for forming on thesubstrate.

[0075] According to the appropriate movement speed shown in FIG. 4, thevalue of (use liquid amount/substrate liquid amount) is about 2.However, vainness of more than the use liquid amount is caused if themovement speed is made higher. Therefore, it is preferred to scan thenozzle at a speed near the appropriate movement speed.

[0076] Incidentally, the movement speed along the file direction whichmakes the processing time (t) minimum (the appropriate movement speed)can be obtained by calculating a value of (v) that makes dt/dv to zerofrom the equation (1), and the movement speed (v) is represented by thefollowing: $\begin{matrix}{v = \sqrt{\frac{La}{2}}} & (2)\end{matrix}$

[0077] The thickness (d) of the liquid film formed on the substratebecomes a value proportional to the value obtained by dividing thedropping amount (W) [ml/sec] per unit time by the speed (v) [m/sec] (d

W/v). Therefore, in order to form a liquid film having a uniformthickness on the substrate, it is necessary to define the droppingamount (W) as an amount proportional to the speed (v). However, in areaswhere no liquid film needs to be formed, for example, an edge of thesubstrate, the dropping amount of the liquid may be reduced or thedropping of the liquid may be stopped.

[0078] In the present embodiment, the liquid is dropped from the singlenozzle. However, in the case that a liquid is dropped from pluralnozzles, the total amount of the liquid dropped from all of the nozzlescorresponds to the dropping amount.

[0079] In the case of processing a rectangle substrate, the speed (v) isdesirably decided from the equation (2) since the application length (L)of the rectangle substrate is constant. However, In the case of adisc-shaped substrate, the speed (v) obtained from the equation (2) doesnot necessarily become an appropriate movement speed since theapplication length (L) changes from 0 to its diameter.

[0080] Table 1 shows the relationship of FIG. 4, that of FIG. 6, andappropriate movement speeds at the portion corresponding to thediameter, which are obtained from the equation (2). TABLE 1 APPROPRIATEACTUAL MOVEMENT APPROPRIATE SPEED IN MOVEMENT ACCELERATION DIAMETER;SPEED; (1 G = 9.8 m/sec²) V₀(m/sec) V(m/sec) (V/V₀)² 12 G 3.40 3.070.815 15 G 3.83 3.42 0.797 18 G 4.20 3.76 0.801

[0081] In the respective cases, the values (V/V0)₂ become about 0.8.Therefore, the appropriate speed (V) for the disc-shaped substrate isobtained from the following equation: $\begin{matrix}\begin{matrix}{v = \sqrt{\frac{0.8 \times {Da}}{2}}} \\{= \sqrt{0.4 \times {Da}}}\end{matrix} & (3)\end{matrix}$

[0082] wherein D represents the diameter of the disc-shaped substrate.

[0083] In order to form a liquid film having a uniform thickness on anydisc-shaped substrate, it is necessary to make the supply amount of aliquid constant since the speed of the dropping unit is constant.However, in areas where no liquid film needs to be formed, for example,an edge of the substrate, the dropping amount of the liquid may bereduced or the dropping of the liquid may be stopped.

[0084] In the present embodiment, the liquid is dropped from the singlenozzle. However, in the case that a liquid is dropped from pluralnozzles, the total amount of the liquid dropped from all of the nozzlescorresponds to the dropping amount.

[0085] Similar graphs about a 12-inch substrate (disc) are shown inFIGS. 6 and 7. Similarly, the values (V/V0)₂ become about 0.8 in thecase of the 12-inch disc. In this way, the values (V/V0)₂ become 0.8regardless of the sizes of the substrates. Thus, the equation (3) can beapplied to all disc-shaped substrates.

[0086]FIG. 8 shows a relationship between the product of substrate sizeand acceleration, that is, D X a, and appropriate movement speed. Usingthis graph, the appropriate movement speed can easily be obtained in thecase of disc-shaped substrates.

[0087] In the present embodiment, the pitch (see FIG. 2) from the centerline of a liquid film dropped from a liquid dropping nozzle to thecenter line of an adjacent film of a dropped liquid is set to 0.33 mm.However, the application of the equation (3) is not limited to thisexample. The equation (3) may be used in other examples if in theexamples their relative movement pitch is 1 mm or less (x mm or less inthe case of nozzles the number of which is x).

[0088] Application of an interlayer dielectric (solid content: 4%) wasperformed at a speed of 3.8 m/sec and an acceleration of 15G accordingto the prior art. The use amount of a liquid at this time was 0.85 cc.However, in a sequence using a movement decided by the deciding methodof the present embodiment, the use amount of a liquid was 0.75 cc. Thus,about 12% of the liquid could be reduced. By this, the amount of theliquid for one process could also be reduced by 12%.

[0089] [Second Embodiment]

[0090] The present embodiment relates to a manner for applying a liquidwhile changing the movement speed of a nozzle and the dropping amount ofthe liquid dependently on the application length of the liquid, using adisc-shaped 12-inch substrate. The application was started from thecenter of the substrate, and was performed at a pitch (p) of 0.33 mmtoward the right direction of the paper (i.e., along the rankdirection). The application reached an end, and subsequently applicationwas performed from a portion shifting by a pitch (p) toward the leftside of the paper from the line applied at the center of the substrateto the left end.

[0091] The movement speed (v) along the file direction at a portionapart from the center of the substrate by np (wherein n is an integer)was decided as the following in relative to the acceleration (a):$\begin{matrix}{v = \sqrt{2a{\sqrt{\left( {D/2} \right)^{2} - {np}^{2}}/2}}} & (4)\end{matrix}$

[0092] The dropping speed (W₀)[ml/sec] along the file direction wasdecided as the following in relative to the dropping speed (W₀) [ml/sec]along the diameter portion. $\begin{matrix}{W = {W_{0} \times {\sqrt{2a{\sqrt{\left( {D/2} \right)^{2} - {np}^{2}}/2}}/\sqrt{{Da}/2}}}} & (5)\end{matrix}$

[0093] Results obtained by making the movement speed and the droppingamount for each of movements along the file direction optimal asdescribed above are shown in FIGS. 9 and 10. Values represented by dotlines are values in the case that movement speed is made optimal (isfixed) by the setting manner described as the first embodiment. A pitchwas set to 0.33 mm. The use amount of a liquid for an interlayerdielectric SOG (solid content: 1.5%) used in the process of the dot linewas 1.7 cc, but the use amount thereof in an actual process was 1.5 cc.The processing time, which was 104 seconds according to the prior art,could be slightly reduced to 102 seconds. Comparison of the use amountsof the liquid is shown in Table 2. Table 2 shows a case in which adisc-shaped 12-inch substrate was used and acceleration (deceleration)was 15G. TABLE 2 PRIOR ART (SET TO SET TO DIAMETER) 0.8 × DIAMETER SETBY LINE USE 1.92 1.70 1.49 AMOUNT(cc) RATIO TO 1 0.89 0.78 PRIOR ART

[0094] As described as the present embodiment, 20% or more of a liquidcan be reduced by using the manner described as the second embodiment(claim 1), as compared with manners in the prior art.

[0095] The present embodiment is an example in which the presentinvention is applied to an interlayer dielectric. The present inventionis not however limited to this example. The present invention can beapplied to various materials such as a resist material, anantireflection material, a dielectric material and a wiring material.

[0096] [Third Embodiment]

[0097] By the above-mentioned conditions, processing time can beshortened and the use amount of a liquid used in the formation of aliquid film can be reduced. However, in the case that theabove-mentioned embodiments are applied to a semiconductor device, it isessential for the formation of a liquid film that the surface of theliquid film is made flat. Therefore, the following will describe aliquid film forming method in which the surface of a liquid film is madeflat.

[0098] As shown in FIG. 11, the contact angle θ an application liquid 13to a substrate 11 to be processed is obtained. The contact angle θ ismeasured as follows. A small amount of a liquid is usually pushed outfrom the tip of a needle of a microsyringe. In the state that the liquidis kept on the tip of the needle by its surface tension, a substrate isbrought near a liquid droplet on the tip of the needle from a lowerspace. If the liquid droplet contacts the substrate, the substrate isimmediately detached from the needle, that is, the substrate is moveddownwards.

[0099] First, the liquid detached from the tip of the needle deforms bygravitation applied to the liquid droplet. This deformation is causedfor 5 seconds after the liquid droplet contacts the substrate and thenthe substrate is detached from the needle. Thereafter, the contact anglechanges as shown in FIGS. 12 and 13. The changes can be roughlyclassified into the following three types: decrease with the passage oftime; very slightly change; and increase with the passage of time. Thesechanges would be caused by a change in interfacial tension between theliquid and the substrate.

[0100] In the liquid whose contact angle decreases with the passage oftime, a solid content or a surfactant in the liquid acts on the surfaceof the substrate. Thus, the liquid has a nature that its interfacialtension becomes weak. In the case that a liquid having such a nature anda substrate is combined, the liquid can easily move on the substrate.For this reason, the liquid is greatly affected by difference inenvironment, for example, environment temperature, forcible airflow, orairflow caused by difference in environment temperature, so that theliquid moves. Therefore, the uniformity of thickness of a solid layerwhich is finally obtained deteriorates.

[0101] Many resists come under such a case. When a liquid which containsethyl lactate as a main solvent and also contains a large amount of asolid content is diluted, a surfactant contained in this resist solutionis also diluted so that the contact angle thereof becomes smaller withthe passage of time. In some cases, it is desired that the amount of thesurfactant is larger than the amount used in spin coating method.

[0102] On the other hand, in the liquid whose contact angle increaseswith the passage of time, a solid content or a surfactant in the liquidacts on the surface of a substrate. Thus, the liquid has a nature thatits interfacial tension becomes strong, or the solid content, thesurfactant or the two condense by strong interfacial tension. In thecase that a liquid having such a nature and a substrate is combined, theliquid condenses on the substrate. As a result, a problem that theliquid cannot be applied to necessary areas arises.

[0103]FIG. 14 shows a relationship between change amount of the contactangle to time after dropping and uniformity (range) of thickness of asolid layer.

[0104] The change amount (dc) of the contact angle to time isrepresented by the following: $\begin{matrix}{{dc} = \frac{\theta_{1} - \theta_{0}}{{\log_{10}\left( t_{1} \right)} - {\log_{10}\left( t_{0} \right)}}} & (6)\end{matrix}$

[0105] wherein the contact angle of a liquid on a substrate at time t₀represents θ₀(degree), the contact angle at time t₁ represents θ₁, to isfrom 5 to 10 seconds, and t₁ is from 10 to about 60 seconds.

[0106] The liquid was applied under the liquid-applying conditionsdescribed as the first and second embodiments. Concerning the thicknessof the formed liquid film, in-plane distribution of the thickness wasmeasured with an optical thickness tester. In the formation ofinterlayer dielectrics or ferroelectric substance films, it is necessaryto make the uniformity of the thickness within 5% (±2.5%). It can beunderstood from FIG. 14 that the change amount (dc) at this time shouldbe |dc|<2.5. Therefore, it was verified that if the change in thecontact angle of the liquid from 5 to 60 seconds after dropping iswithin 2.5 degrees, the in-plane uniformity of the liquid film is within5%. However, in order to make the liquid film flatter, the change in thecontact angle from 5 to 60 seconds after dropping is preferably within 2degrees.

[0107] In order to suppress the change in the contact angle of a liquidto a substrate after dropping, it is advisable that the kind and amountof a solvent, a solid content and a surfactant in a solution isappropriately adjusted.

[0108] In the present embodiment, ethyl lactic was used as the solvent,and 1-5% by weight of a KrF resist was used as the solid content. Thecohesiveness which became stronger as the percentage of this resist wasraised was overcome by increasing the added amount of the surfactantdependently on the amount (% by weight) of the resist.

[0109] It is preferred that the contact angle of a liquid to a substrateis less than 20° for 5 seconds after dropping the liquid. If the contactangle is 20° or more, cohesion is caused when the liquid film is dried.Thus., a complete film cannot be formed.

[0110] The present embodiment can be applied to all applicationmaterials, for example, a resist material, an antireflection material, adielectric material, and a wiring material. The application method ofthe present invention can be applied to not only manners of supplying anapplication liquid as parallel lines and then spreading the liquid toform a liquid film, as seen in the first and second embodiments, butalso manners of supplying an application liquid in the form of a spiralfrom the substantial center of a round substrate to the peripherythereof or from the periphery to the center, and then spreading theliquid to form a liquid film. It was also verified that in applicationmethods using a capillary phenomenon, which have been hitherto carriedout, better uniformity of film thickness can be obtained.

[0111] In the present embodiment, it is preferred that the average filmthickness of a liquid film obtained by spreading a liquid is 20 μm orless. If the film thickness is larger than 20 μm, fluidity is generatedin the liquid film so that/the uniformity thereof deteriorates.

[0112] [Fourth Embodiment]

[0113] An extrafine nozzle is reciprocated at a speed of lm/sec along afile direction on a substrate. At ends of the reciprocation motion, thesubstrate is successively moved along a rank direction. Thus, a liquidis dropped in the form of a line drawn with a single stroke of thenozzle. In this way, a resist is dropped on the whole surface (diameter:200 mm) of the substrate. In the first and second embodiments in which aliquid film of the resist is formed on the whole surface of thesubstrate in the manner mentioned just above, the distance between astep end portion of the substrate and the end of the liquid film waschanged dependently on flowing distance from the formation of the liquidfilm from the dropped resist to a drying step. Specifically, thedistance between the step end portion of the substrate and the end ofthe liquid film is set up to a distance that the end of the flowingliquid film just reached the step end portion of the substrate.

[0114] The step end portion of the substrate will be described,referring to FIG. 15. As shown in FIG. 15, in the case that an undercoatfilm 152 and an antireflection film 153 are made on a Si wafer 151, stepend portions are an end of the Si wafer 151, a level-differentiatingdifference portion between the Si wafer 151 and the undercoat film 152,and ends of the undercoat film 152 and the antireflection film 153. Inthe case that a liquid film is formed on an undercoat having unevenness,a level-differentiating portion between the outmost portion of theundercoat film and a film outside it or a substrate is defined as a stepend portion.

[0115] In the case that a liquid film 30 μm in thickness made from aliquid resist is formed on a substrate, the liquid flows by 3 mm at adropping start side during stand-by time until drying processing and theliquid flows by 1 mm at a dropping finish side during the stand-by timeuntil the drying processing. Therefore, in the present embodiment, adropping start position was set to a position inward by 3 mm from theend of the substrate and a dropping finish position is set to a positioninward by 1 mm from the end of the substrate. Considering the timingthat the flowing end of the liquid film reaches the end of thesubstrate, the distance between other ends of the substrate and the endof the liquid film is gradually made smaller within the range of 3 to 1mm over positions from the dropping start position to the droppingfinish position (FIG. 16).

[0116]FIG. 16 is a view for explaining a liquid film forming methodaccording to the fourth embodiment of the present invention. As/shown inFIG. 16, a resist dropping area R is sectioned in a substrate 11. In thearea R, the distance between the end of the substrate and the end of theliquid film gradually becomes smaller within the range of 3 to 1 mm overpositions from a dropping start position to a dropping finish position.

[0117]FIG. 17 is a sectional view of the state that a resist is appliedonto the resist dropping area R in the substrate of the presentembodiment. In FIG. 17, a resist formed by a conventional method issimultaneously shown for reference. The sectional view shown in FIG. 17corresponds to a section taken along A-A′ line of FIG. 16.

[0118] After the liquid film was formed on the whole surface of thesubstrate by the present method, a solvent in the liquid film wasremoved by drying under reduced pressure to form an application film 30nm in thickness. At last, the film was subjected to heating treatment at140° C. with a baker, so as to stabilize the application film.

[0119] The distribution of thickness of the formed resist film wasmeasured in an optical manner. FIGS. 18A and 18B are views each of whichshows a distribution of the film thickness. FIG. 19 shows positionswhere the distribution of the film thickness was measured. FIG. 18Ashows the distribution of the film thickness along the X-X′ line of FIG.19, and FIG. 18B shows the distributions of the film thickness along theY1-Y1′ and Y2-Y2′ lines. FIGS. 18A and 18B also show a distribution ofthickness of an application film formed by a conventional method inwhich the distance between the end of a liquid film and the end of asubstrate was constantly set to 2 mm over positions from an applicationstart side to an application finish side.

[0120] As shown in FIGS. 19A and 19B, in the distribution of thethickness of the application film formed by the conventional method, thefilm thickness increases highly at the application start side and thefilm thickness decreases gently at the application finish side. Thereason why such a distribution of the film thickness is produced is thatthe flowing distance of the liquid during the time from the formation ofthe liquid film to a drying processing is different between theapplication start side and the application finish side.

[0121] This fact will be described, referring to FIGS. 20 and 21. FIGS.20A, 20B, 21A and 21B show states of the end of a substrate and the endof a liquid film in the case of a conventional liquid film formingmethod. FIG. 20A shows a state of the end of the substrate and the endof the liquid film at an application start side at the time of dropping,and FIG. 20B shows a state of the end of the substrate and the end ofthe liquid film at the application start side at the time of finishingthe formation of the liquid film. FIG. 21A shows a state of the end ofthe substrate and the end of the liquid film at an application finishside at the time of the dropping, and FIG. 21B shows a state of the endof the substrate and the end of the liquid film at the applicationfinish side at the time of finishing the formation of the liquid film.

[0122] Stand-by time until the drying process is longer at theapplication start side than at the application finish side. Thus, theflowing distance of the liquid becomes longer accordingly. In the casethat at this time the distance up to the end of the substrate is smallerthan the flowing distance, the flow of the liquid is stopped at the endof the substrate 11 so that the thickness of the liquid film 13increases with subsequent flow of the liquid, as shown in FIGS. 20A and20B.

[0123] On the other hand, the liquid is subjected to the given dryingprocessing at the application finish side immediately after theformation of the liquid film, so that the flowing distance becomessmaller at this side than at the application start side. In the casethat at this time the distance up to the end of the substrate is largerthan the distance of flow, the thickness of the liquid film gentlybecomes thinner toward the end of the liquid film at a given surfacecontact angle as shown in FIGS. 21A and 21B.

[0124] As described above, in this conventional method, fluidity of theliquid after being dropped is ignored and the above-mentioned distanceis set constant from the dropping start side to the dropping finishside. For this reason, an abnormality of the film thickness arises asshown in FIGS. 20B and 21B.

[0125] On the other hand, as in the present embodiment, in the case thatconsidering the fluidity of the liquid after being dropped, the distancebetween the end of the substrate and the end of the liquid film ischanged over positions from the dropping start side to the droppingfinish side in the manner that the end of the dried liquid film justreaches the end of the substrate, it is possible to realize a symmetricand uniform distribution of the thickness of the applied film over allperipheral portions of the substrate. When the liquid film reaches theend of the substrate 11, contact angle of the end of the liquid film 13becomes large (for example, θ1→θ2), as shown in FIG. 22. In this case,therefore, the liquid film comes to have a steeper edge than the casethat the liquid film does not reach the end of the substrate 11, asshown in FIG. 22.

[0126] The present embodiment can be applied to all applicationmaterials, for example, a resist material, an antireflection material, adielectric material, and a wiring material. The application method ofthe present invention can be applied to not only the scope described asthe present embodiment but also an embodiment in which a slit-formdropping nozzle having the same width as a substrate is used, or a scanapplication method in which a meniscus is produced between a droppingnozzle and a substrate. The shape of a substrate to be processed is notlimited to a circle as shown in the above-mentioned embodiment. Arectangle substrate, such as a reticle or a liquid crystal substrate,may be used. In the case of the rectangle substrate as shown in, forexample, FIG. 23, a liquid is dropped onto a liquid applying area R setup in a substrate 21.

[0127] The distance between the area where a liquid is dropped and thestep end portion of a substrate appropriately set up dependently onphysical properties of the liquid and conditions of the substrate withinthe scope of the subject matter of the present embodiment that thisdistance is changed from a large value to a small value over positionsfrom a dropping start side to a dropping finish side.

[0128] In the present embodiment, the area where the liquid is droppedis decided in the manner that the liquid film reaches the step endportion of the substrate by fluidity of the liquid. Further, thedistance between the area where the liquid is dropped and the step endportion of the substrate is changed from a large value to a small valueover positions from the dropping start side to the dropping finish side.However, the liquid film may not reach the step end portion of thesubstrate. In the case that the liquid film does not reach the step endportion, it is not essential that the distance between the area wherethe liquid is dropped and the step end portion of the substrate ischanged from a large value to a small value over positions from thedropping start side to the dropping finish side.

[0129] [Fifth Embodiment]

[0130] An extrafine nozzle is reciprocated at a speed of lm/sec along afile direction on a substrate. At the same time, the substrate issuccessively moved along a rank direction. Thus, a, liquid is dropped inthe form of a line drawn with a single stroke of the nozzle. In thisway, the resist is dropped on the whole surface (diameter: 200 mm) ofthe substrate. In the first and second embodiments in the mannermentioned just above, a DUV resist is formed. In this case, according toconventional manners, the thickness of the liquid film has been set to30 μm (line pitch along the rank direction: 0.3 mm). However, in thepresent embodiment, the liquid film was made to have a thickness of 20or 15 μm, which was thinner than the thickness based on the conventionalmanners.

[0131] The thickness of the liquid film was controlled by changing aline pitch. In the case of 20 μm and 15 μm, the line pitches were 0.6and 0.8 mm, respectively. The distance between the end of the substrateand the end of the liquid film was constantly set to 2 mm over positionsfrom a dropping start portion to a dropping finish portion. The liquidfilms were formed on the whole of the substrates to have the respectivetarget thicknesses. Thereafter, solvents in the liquid films wereremoved by drying under reduced pressure, to form application filmshaving thicknesses of 300 nm, 200 nm and 150 nm, respectively. At last,the films were subjected to heating treatment at 140° C. with a baker tostabilize the application films.

[0132] The distributions of thickness of the respective formed resistfilms were measured in an optical manner. FIG. 24 shows measured resultsthereof. FIG. 24 also shows uniformity of the thicknesses of theapplication films except abnormal areas of the film thickness at theperipheral portion of the substrates.

[0133] As shown in FIG. 24, in the distribution of the thickness of theapplication film formed from the liquid film 30 μm in thickness by theconventional method, the film thickness increased highly at theapplication start side and the film thickness decreased gently at theapplication finish side. The reason why such a distribution of the filmthickness is produced is that the liquid film flows during the time fromthe formation of the liquid film to the drying processing.

[0134] The following will describe the relationship between thickness ofthe liquid film and fluidity thereof according to a conventional filmforming method and the film forming method of the present embodimentwith reference to FIGS. 25A and 25B. FIG. 25A is a view for explainingthis relationship according to the conventional film forming method.FIG. 25B is a view for explaining this relationship according to thefilm forming method of the present embodiment.

[0135] In the case that the thickness of the liquid film was 30 μm bythe conventional method, the thickness was larger than the thicknessthat the substrate could keep as shown in FIG. 25A when the liquid wasdropped to form the liquid film. Therefore, flow was remarkably caused.In the state that such flow is easily caused, the liquid film is easilyaffected by environment at the time of the application. Thus, control ofthe film thickness at the center of the substrate becomes difficult, anduniformity deteriorates.

[0136] On the other hand, when the liquid film is made thinner to have athickness of 20 μm or 15 μm as in the present invention, the liquid filmis easily kept on the substrate by surface tension of the liquid asshown in FIG. 25B. Thus, when the liquid film is formed, flow is easilycaused. Accordingly, abnormality of the film thickness at the peripheralportion of the substrate (in particular application start and finishportions), which is caused by flow, is overcome. Furthermore, the flowof the liquid is not easily caused even if the liquid is affected byexternal environmental factors in the application and drying steps. As aresult, uniformity becomes good.

[0137] The present embodiment can be applied to all applicationmaterials, for example, a resist material, an antireflection material, adielectric material, and a wiring material. The application method ofthe present invention can be applied to not only the scope described asthe present embodiment but also an embodiment in which a slit-formdropping nozzle having the same width as a substrate is used, or a scanapplication method in which a meniscus is produced between a droppingnozzle and a substrate. The shape of a substrate to be processed is notlimited to a circle as shown in the above-mentioned embodiment. Arectangle substrate, such as a reticle or a liquid crystal substrate,may be used. The thickness of the liquid film at the time of dropping isnot limited to that in the present embodiment. The scan speed of thenozzle, the amount of the jetted-out liquid, physical properties of theused liquid, and conditions of the substrate may be changed. They may beappropriately set up so far as they do not depart from the scope of thesubject matter of the present embodiment

[0138] The present invention is not limited to the above-mentionedembodiments, and may be varied within the scope of the subject matter ofthe present invention.

[0139] Additional advantages and modifications will readily occur tothose skilled in the art. Therefore, the invention in its broaderaspects is not limited to the specific details and representativeembodiments shown and described herein. Accordingly, variousmodifications may be made without departing from the spirit or scope ofthe general inventive concept as defined by the appended claims andtheir equivalents.

What is claimed is:
 1. A liquid film forming method of dropping a liquidadjusted to be spread into a give amount on a substrate to be processedfrom a dropping nozzle or dropping nozzles of a dropping unit onto thesubstrate, and then moving the dropping unit and the substraterelatively while keeping the liquid dropping on the substrate, so as toform a liquid film on the substrate, wherein the relative movement ofthe dropping unit and the substrate is composed of straight movementalong a file direction in which the dropping unit passes from one endside of/the substrate through an upper space of the substrate to theother end side of the substrate, and movement along a rank directionoutside the substrate, movement length along the file direction is thesum of dropping length (L) over the substrate and distance of anacceleration/deceleration section, and movement speed (v) along the filedirection over the substrate is defined dependently on the square rootof the product of the dropping length (L) and the absolute value ofacceleration/deceleration (a) within the acceleration/decelerationsection.
 2. The liquid film forming method according to claim 1, whereindropping amount (W) from the dropping nozzle or the dropping nozzles ofthe dropping unit positioned over the substrate is defined dependentlyon an amount proportional to the Movement speed (v).
 3. The liquid filmforming method according to claim 1, wherein the dropping unit hasplural dropping nozzles and the dropping amount (W) is the total amountof the liquid dropped from all of the dropping nozzles.
 4. The liquidfilm forming method according to claim 1, wherein the liquid is any oneselected from an antireflection material, a resist material, a lowdielectric material, an insulating material, a wiring material and ametal paste.
 5. The liquid film forming method according to claim 1,wherein the liquid film is formed, using the liquid having a nature thatwhen a minute amount of the liquid is dropped onto a minute area of thesubstrate, a change amount of a contact angle of the liquid to thesubstrate is within ±2 degrees during a time from 5 seconds to 60seconds after the dropping of the liquid.
 6. A liquid film formingmethod of dropping a liquid adjusted to be spread into a give amount ona disc-shaped substrate which is to be processed and has a diameter (D)has from a dropping nozzle or dropping nozzles of a dropping unit abovethe substrate, and then moving the dropping unit and the substraterelatively while keeping the liquid dropping on the substrate, so as toform a liquid film on the substrate, wherein the relative movement ofthe dropping unit and the substrate is composed of straight movementalong a file direction in which the dropping unit passes from one endside of the substrate through an upper space of the substrate to theother end side of the substrate, and movement along a rank directionoutside the substrate, and movement speed (v) along the file directionis defined dependently on the square root of the product of constant0.4, the diameter (D) of the substrate, and the absolute value ofacceleration/deceleration (a) before and after the time when themovement speed (v) is given.
 7. The liquid film forming method accordingto claim 6, wherein dropping rate amount from the dropping nozzle or thedropping nozzle of the dropping unit over the substrate is constant. 8.The liquid film forming method according to claim 6, wherein thedropping unit has plural dropping nozzles and the dropping amount is thetotal amount of the liquid dropped from all of the dropping nozzles. 9.The liquid film forming method according to claim 6, wherein the liquidis any one selected from an antireflection material, a resist material,a low dielectric material, an insulating material, a wiring material anda metal paste.
 10. The liquid film forming method according to claim 6,wherein the liquid film is formed, using the liquid having acharacteristic that when a minute amount of the liquid is dropped onto aminute area of the substrate, a change amount of a contact angle of theliquid to the substrate is within ±2 degrees during a time from 5seconds to 60 seconds after the dropping of the liquid.
 11. A liquidfilm forming method of dropping a liquid adjusted to be spread into agive amount on a substrate to be processed from a dropping nozzle ordropping nozzles of a dropping unit onto the substrate, and then movingthe dropping unit and the substrate relatively while keeping the liquiddropping on the substrate, so as to form a liquid film on the substrate,wherein the relative movement of the dropping unit and the substrate iscomposed of straight movement along a file direction in which thedropping unit passes from one end side of the substrate through an upperspace of the substrate to the other end side of the substrate, andmovement along a rank direction outside the substrate, or is composed ofspiral movement in which the dropping unit goes from the substantialcenter of the substrate to the periphery thereof or from the peripheryof the substrate to the substantial center thereof, and a change amountof a contact angle of the liquid to the substrate is within +2 degreesduring a time from 5 seconds to 60 seconds after the dropping of theliquid when a minute amount of the liquid is dropped onto a minute areaof the substrate.
 12. The liquid film forming method according to claim11, wherein control of the change amount of the contact angle of theliquid dropped onto the substrate to the substrate within ±2 degrees isattained by adjusting the ratio of a surfactant to a solvent and anapplication agent constituting the liquid.
 13. A liquid for applicationused in a liquid film forming method of dropping the liquid adjusted tobe spread into a give amount on a substrate to be processed from adropping nozzle or dropping nozzles of a dropping unit onto thesubstrate, and then moving the dropping unit and the substraterelatively while keeping the liquid dropping on the substrate, so as toform a liquid film on the substrate, comprising a solvent, anapplication agent, and a surfactant, wherein the ratio of the surfactantto the solvent and the application agent is adjusted in such a mannerthat when a minute amount of the liquid is dropped onto a minute area ofthe substrate, a change amount of a contact angle of the liquid to thesubstrate is within 2 degrees during a time from 5 seconds to 60 secondsafter the dropping of the liquid.
 14. A liquid film forming method ofdropping a liquid adjusted to be spread into a give amount on asubstrate to be processed from a dropping nozzle or dropping nozzles ofa dropping unit onto the substrate, and then moving the dropping unitand the substrate relatively while keeping the liquid dropping on thesubstrate, so as to form a liquid film on the substrate, wherein therelative movement of the dropping unit and the substrate is composed ofstraight movement along a file direction in which the dropping unitpasses from one end side of the substrate through an upper space of thesubstrate to the other end side of the substrate, and movement along arank direction outside the substrate, or is composed of spiral movementin which the dropping unit goes from the substantial center of thesubstrate to the periphery thereof or from the periphery of thesubstrate to the substantial center thereof, and a dropping area isdefined in such a manner that when the liquid film is spread by itsfluidity, the liquid does not extend over a boundary step of thesubstrate film in the edge area of the substrate.
 15. A liquid filmforming method of dropping a liquid adjusted to be spread into a giveamount on a substrate to be processed from a dropping nozzle or droppingnozzles of a dropping unit onto the substrate, and then moving thedropping unit and the substrate relatively while keeping the liquiddropping on the substrate, so as to form a liquid film on the substrate,wherein the relative movement of the dropping unit and the substrate iscomposed of straight movement along a file direction in which thedropping unit passes from one end side of the substrate through an upperspace of the substrate to the other end side of the substrate, andmovement along a rank direction outside the substrate, or is composed ofspiral movement in which the dropping unit goes from the substantialcenter of the substrate to the periphery thereof or from the peripheryof the substrate to the substantial center thereof, and relationshipbetween the distance from a dropping start position along the rankdirection to a boundary step of the edge of the substrate and that froma dropping finish position along the rank direction to the boundary stepof the edge thereof is set so that the former distance is large and thelatter distance is small, and the distance between an end of the liquidfilm along the file direction and the boundary step of the edge is setso as to gradually become smaller from the dropping start position tothe dropping finish position.
 16. The liquid film forming methodaccording to claim 15, wherein the distance between the end of theliquid film and the boundary Step of the edge is decided dependently onsuch a distance that the liquid flows on the substrate after thedropping of the liquid on the substrate.
 17. The liquid film formingmethod according to claim 15, wherein the distance between the end ofthe liquid film and the boundary step of the edge is defined as adistance that the end of the liquid film reaches the end of thesubstrate by flow.
 18. A liquid film forming method of dropping a liquidadjusted to be spread into a give amount on a substrate to be processedfrom a dropping nozzle or dropping nozzles of a dropping unit onto thesubstrate, and then moving the dropping unit and the substraterelatively while keeping the dropped liquid on the substrate, so as toform a liquid film on the substrate, wherein the relative movement ofthe dropping unit and the substrate is composed of straight movementalong a file direction in which the dropping unit passes from one endside of the substrate through an upper space of the substrate to theother end side of the substrate, and movement along a rank directionoutside the substrate, or is composed of spiral movement in which thedropping unit goes from the substantial center of the substrate to theperiphery thereof or from the periphery of the substrate to thesubstantial center thereof, and the thickness of the liquid film isdecided in the manner that the liquid film formed on the substrate flowsto an extent which is substantially decided by gravitation applied tothe liquid film.
 19. The liquid film forming method according to claim18, wherein the thickness of the liquid film is set to 20 μm or less.